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The surface recombination velocities (SRVs) of minority carriers on crystalline silicon (c-Si) surfaces are remarkably reduced by applying radical treatment at less than 150°C in a catalytic chemical vapor deposition (Cat-CVD) system prior to the deposition of surface-passivating amorphous Si (a-Si) films. Hydrogen (H) radical treatment on c-Si surfaces is found to be effective for improvement in the SRVs. The effect of the H radical treatment is significantly affected by the temperature of a catalyzer (Tcat) used for the catalytic cracking of H2 molecules, and the Tcat should be moderated in order to effectively generate H radicals and not to induce the etching of c-Si surfaces by H radicals. The addition of a slight amount of PH3 gas during the H radical treatment drastically improves the SRVs, and microwave photoconductivity decay (μ-PCD) measurement yields the effective carrier lifetimes (teff) of approximately 4 ms for n-type Si wafers after the PH3-adding radical treatment and following deposition of a-Si films. This remarkably high teff corresponds to a SRV of as low as 3-4 cm/s even assuming no carrier recombination in Si bulk. The effect of PH3 addition on SRV is fully understood as the doping of P atoms into Si surfaces and resulting downward band bending.